A fruit by any other name would smell as rotten

We live in a world full of signals. We are constantly bombarded with exciting new combinations of light, sound, taste, smell, and texture. Ultimately our brains interpret these sensations to form what we call reality. However, as it turns out, human beings are only able to perceive a small slice of reality: there are many smells which, for better or worse, we can never smell, and we can only see a tiny slice of the colors light has to offer (we refer to this small portion of wavelengths as the “visible spectrum”).

Insects exist on a different slice of reality. Even with their smaller brains, insects are able to see, taste, and smell many things that even the most anthropocentric among us cannot. As Dr. Zain Syed described in his Entomology Department colloquium seminar, the ways insects smell what we cannot are fascinating, and how we can take advantage of that fact can be very important.

Like all entomologists, Dr. Syed breaks the life cycle of insects into distinct stages of development. For the spotted wing drosophila (SWD or Drosophila suzukii), a serious fruit pest throughout the globe, the adult females cycle from mating on

Dr. Zain Syed sampling the scent a local stink bug on the Great Wall of China.

The spotted wing drosophila is an aptly named pest of fruit (photo by Martin Hauser).

When the female is ready to mate, she emits and senses a range of conspecific odors, commonly referred to as sex pheromones; when she is ready to lay eggs, she seeks the odors of fresh fruit. Just as you may follow the smell of fresh cookies into the kitchen, flies can recognize when objects produce scents that are important to them. Dr. Syed and his research team can further break this down into two parts: what does the fly smell and how do they smell it?

As it turns out, flies do not base their behavior on the smell of the fruit: they base it on the smell of the yeast growing on the fruit. When yeasts are removed from fruit, the flies do not know where to go. Dr. Syed’s team took a sample of yeasts abundant in fruit and associated SWD flies and found that SWD choose certain yeasts over others, but why?

To answer this question, they sampled the odors that were produced by his yeasts using solid-phase microextraction (SPME) to see if they were different. They were in fact different – qualitatively and quantitatively - with each yeast isolate producing a very complex and wide range of odorant repertoire. Approaching the point of despair at interpreting all of his data, a statistician swooped in to save the day. The statistician was able to distinguish between the yeasts based solely on the odors they produce.

Since it is unlikely the flies have access to SPME and a statistician while searching for rotting fruit in the field, Dr. Syed is working to determine what chemicals in these odors flies use to identify these yeasts during each stage of their lifecycle. He then plans to use these chemicals to create traps for the Spotted Wing Drosophila that take advantage of their unique attraction to the smell of yeast growing on fresh fruit.

Solid-phase microextraction (SPME) in process for of one of Dr. Syed’s yeast isolates.

Read more about Dr. Syed’s Work
 
Scheidler, N. H., Liu, C., Hamby, K. A., Zalom, F. G., & Syed, Z. (2015). Volatile codes: Correlation of olfactory signals and reception in Drosophila-yeast chemical communication. Scientific reports, 5, 14059.

Hickner, P. V., Rivaldi, C. L., Johnson, C. M., Siddappaji, M., Raster, G. J., & Syed, Z. (2016). The making of a pest: Insights from the evolution of chemosensory receptor families in a pestiferous and invasive fly, Drosophila suzukii. BMC genomics, 17(1), 648.
 
About the author:
 
Brian Lovett is a PhD student in Dr. Raymond St. Leger’s Lab studying mycology and genetics in agricultural and vector biology systems. He is currently working on projects analyzing mycorrhizal interactions in agricultural systems, the transcriptomics of malaria vector mosquitoes, and the genomes of entomopathogenic fungi.
 
Brief Summary:
 
At the first Entomology colloquium of the Spring 2017 semester, Dr. Zain Sayed described his work on the agricultural pest spotted wing drosophila. His work unravels how female flies use odors from yeasts growing on fruit to find their mates.